The present invention relates generally to flow cytometers. More particularly, the present invention relates to portable flow cytometers that sense optical properties of microscopic biological particles in a flow stream.
Flow cytometry is a technique that is used to determine certain physical and chemical properties of microscopic biological particles by sensing certain optical properties of the particles. To do so, the particles are arranged in single file using hydrodynamic focussing within a sheath fluid. The particles are then individually interrogated by a light beam. Each particle scatters the light beam and produces a scatter profile. The scatter profile is often identified by measuring the light intensity at different scatter angles. Certain physical and/or chemical properties of each particle can then be determined from the scatter profile.
Flow cytometry is currently used in a wide variety of applications including hematology, immunology, genetics, food science, pharmacology, microbiology, parasitology and oncology, to name a few. A limitation of many commercially available flow cytometer systems is that they are relatively large bench top instruments that must remain in a central laboratory environment. Accordingly, the use of such flow cytometers is often not available in remote locations or for continuous hematological monitoring.
The present invention overcomes many of the disadvantages of the prior art by providing a portable or wearable cytometer that can be used at remote locations, such as at home or in the field. Such a flow cytometer may help improve healthcare of patients by providing detailed individual hematological evaluation and uncovering statistical trends. By detecting an infection early, the infection may be more readily treatable.
In military applications, the portable cytometer of the present invention may help save lives by providing early detection of infection due to biological agents. It is known that expanded activity in the biological sciences has increased the probability of accidental exposure to dangerous biological agents. The ease of manufacturing such agents also raises a serious threat to their use by terrorists, regional powers or developing third world nations. The lack of safeguards in international agreements outlawing biological warfare, and compelling evidence that those agreements may have been violated, reinforces the need for a strong capability for biological defense. During Desert Storm, American forces were not prepared to operate in a biological environment. Pre-exposure detection of pathogen agents, as well as post-exposure detection of incipient infections had to be used cooperatively to ensure efficient protection during biological warfare.
As part of the body""s natural defense against antigens, the white blood cell count increases at the onset of infection. There are several types of white blood cells including neutrophils, lymphocytes, monocytes, eosinophils and basofils. Lymphocytes create antibodies that attack the invaders and mark them for destruction by the neutrophils and macrophages. In an individual without chronic diseases (such as tuberculosis or cancer), an increase in the percentage of lymphocytes in the overall white cell count is an indication of a viral infection. On the other side, an increase in the percentage of the neutrophils is an indication of a developing bacterial infection. Through counting of neutrophils and lymphocytes, a clear infection warning can be issued with differentiation between viral or bacterial causes.
The first clinical symptoms of infection from some bacterial agents such as bacillus anthrax appear after one to six days. In 99% of the cases, patients showing symptoms from anthrax cannot be treated, and will most likely die. However, if treatment is given before the first symptoms appear, most patients can be successfully treated. Accordingly, it would be highly desirable to provide an early alert and potential therapeutic intervention for hematologic abnormalities before symptoms occur. In many cases, such an early alert and treatment may greatly improve the outcome for many patients.
In one illustrative embodiment of the present invention, a portable cytometer is provided for identifying and/or counting selected particles in a fluid sample such as a blood sample. One illustrative portable cytometer includes a fluid receiver for receiving the fluid sample. One or more reservoirs are provided for storing supporting fluids such as lyse and sheath fluids. For many commercial flow cytometer systems, a precision fluid driving system is used for providing precise pressures to the fluids. A limitation of this approach is that precision fluid driving systems can be bulky, complex and may require significant power.
To avoid many of these limitations, one illustrative embodiment uses a non-precision fluid driver that is controlled by a closed loop feedback path. The non-precision fluid driver is coupled to the fluid receiver and the various supporting fluid reservoirs, and applies separate pressures to the sample fluid and the supporting fluids. To control the velocity of the sample fluid and the supporting fluids, one or more valves are coupled to the fluid driver. The valves are used to regulate the non-precision pressures that are applied to the sample fluid and the supporting fluids by the non-precision fluid driver.
To complete the feedback loop, flow sensors are provided downstream of the fluid driver to measure the fluid velocity of the sample fluid and the supporting fluids. A controller or processor receives the signals from the flow sensors, and adjusts the appropriate valves so that the desired fluid velocities of the sample fluid and supporting fluids are achieved. The flow sensors are preferably thermal anemometer type flow sensors.
In one embodiment, the non-precision fluid driver is manually powered. A manually powered fluid driver may include, for example, a bulb with check valve or a plunger. In either case, the manually generated pressure is preferably provided to a first pressure chamber. A first valve is then provided for controllably releasing the pressure in the first pressure chamber to a second pressure chamber. A second valve may be provided in the second pressure chamber for controllably venting the pressure in the second pressure chamber. The controller opens the first valve when the fluid flow in the downstream fluid stream drops below a first predetermined value and opens the second valve when the fluid flow in the downstream fluid stream increases above a second predetermined value. Each valve is preferably an array of electrostatically actuated microvalves that are individually addressable and controllable.
The controlled sample fluid and supporting fluids are provided to a fluidic circuit. The fluidic circuit performs hydrodynamic focusing, which causes the desired particles to fall into single file along a core stream surrounded by a sheath fluid. One or more light sources provide light through the flow stream, and one or more light detectors detect the scatter profile of the particles in the flow stream. A processing block uses the output signals from the light detectors to identify and/or count selected particles in the core stream.
The portable cytometer may be provided in a housing sufficiently small to be xe2x80x9cwearablexe2x80x9d. In one embodiment, the housing is sized similar to a wrist watch. The wearable housing may include, for example, a base, a cover, and a hinge that secures the base to the cover. The non-precision fluid driver and regulating valves may be incorporated into the cover, while the fluid reservoirs, flow sensors and fluidic circuit may be incorporated into a removable cartridge that is inserted into the housing. Preferably, the fluidic circuit dilutes the blood sample, performs red cell lysing, and performs hydrodynamic focusing for flow and core stream formation. The light sources are preferably situated in either the base or the cover, and aligned with the flow stream of the removable cartridge. The light detectors are preferably provided generally opposite the light sources. The processor and batteries may be provided in either the base or the cover of the housing.
The light sources may include a linear array of first light sources along a first light source axis. The first light source axis is preferably rotated relative to the central axis of the flow stream. A lens may be provided adjacent each light source to focus the light at the particles in the core stream. A first set of light detectors may then be placed in-line with each of the light source. Such an arrangement can be used to determine, for example, the alignment and width of the core stream within the flow stream. If the core stream of particles is not in proper alignment, the controller can adjust the fluid velocity of the sample fluid or one of the supporting fluids to bring the core stream into alignment. The first set of light detectors may also be used to detect the velocity and size of each particle, as well as the number of particles.
A second set of the light sources may be provided along a second light source axis. A lens may be provided adjacent each light source to focus the light at the particles in the core stream. A second set of light detectors may then be placed on either side of the in-line position of each light source for measuring the small angle scattering (SALS) produced by selected particles in the flow stream.
The second set of light sources may also be used in conjunction with the first set of light sources to determine the time-of-flight or velocity of the particles in the flow stream. By knowing the velocity of the particles, small variations in the flow rate caused by the fluid driver can be minimized or removed by the controller.
A third set of light sources may be provided along a third light source axis. A lens may be provided adjacent each light source to provide collimated light to the flow stream. Annular light detectors are then preferably placed opposite the light sources for measuring the forward angle scattering (FALS) produced by the selected particles in the flow stream. Each of the first, second and third set of light sources preferably include an array of lasers such as Vertical Cavity Surface Emitting Lasers (VCSEL) fabricated on a common substrate. Each of the first, second and third set of light detectors preferably include an array of photo detectors such as p-i-n photodiodes, GaAs photodiodes with integrated FET circuits, Resonant Cavity Photo Detectors (RCPD), or any other suitable light detector.
The selected particles are preferably neutrophils and/or lymphocytes white blood cells. By examining the scatter profile of each particle, the portable cytometer of the present invention preferably identifies and counts the neutrophils and lymphocytes in a blood sample, and provide a clear infection warning with differentiation between viral and bacterial causes.